lsatin (2,3-dioxoindole) has been reacted with N-(6-chloro benzothiazol-2-yl) thiosemicarbazide to form Schiff base and the N-Mannich bases of the above Schiff base were synthesized by reacting with formaldehyde and several secondary amines. The chemical structures of N-Mannich bases have been confirmed by means of IR, 1H-NMR data and by elemental analysis. Investigation of antimicrobial activity of compounds was done by agar dilution method against 25 pathogenic bacteria, 8 pathogenic fungi and anti-HIV activity against replication of HIV-1 (Ill B) in MT-4 cells. Among the compounds tested 1-[N,N-dimethylaminomethyl] isatin-3-[1'(6"-chlorobenzothiazoI-2"-yl) thiosemicarbazone] showed the highest antimicrobial activity.